Frequency modulation the amplitude

relation back absolute relative oftenness inflection the premiumINTRODUCTIONIn frequency changeover the premium is unbroken unending and the frequency is modulate by the bountifulness of the modulating bespeak. The modulation magnate for fm is m = maximum frequency deviation/modulating frequency. FM symbol bear be represented as-v = ac sin(wct + m sin wmt )ABSTRACT oftenness modulation is a guinea pig of modulation where the frequency of the mailman is varied in accordance with the modulating signal. The amplitude of the pallbearer remains constant.The information-bearing signal (the modulating signal) changes the instantaneous frequency of the carrier. Since the amplitude is kept constant, FM modulation is a low- folie process and provides a high property modulation technique which is use for music and speech in hi- fidelity disperses.In addition to hi-fidelity radio transmission, FM techniques are employ for other consequential con entirenesser applications much(prenominal) as audio synthesis and recording the luminance percentage of a video signal with little torment.There are some(prenominal) devices that are capable of generating FM signals, such as a VCO or a reactance modulator.Frequency changeover is abbreviated FM.DefinitionsAn important concept in the understanding of FM is that of frequency deviation. The amount of frequency deviation a signal experiences is a measure of the change in vector make frequency from the symmetricalness frequency of the sender. The rest frequency of a transmitter is defined as the output frequency with no modulating signal applied. For a transmitterwith linear modulation characteristics, the frequency deviation of the carrier is at a epoch proportional to the amplitude of the applied modulating signal.Mathematical Analysis of FMAs was done with AM, a mathematical analysis of a high-frequency hell cockle, modulated by a single tone or frequency, allow be use to yield information about th e frequency destinys in an FM wave, FM exponent relations, and the bandwidth of an FM signal. From the definition of frequency deviation, an comparability potbelly be written for the signal frequency of an FM wave as a function of timefsignal = fC + kf eM(t) = fC + kf EM sin?MtAnd transposition of d = kf EM yieldsfsignal = fC + d sin?MtBut what does this equation indicate? It implementms to be saying that the frequency of the transmitter is varying with time. This brings up the same type of problem that was observed when we looked at a time display of AM and then performed a mathematical analysis in an attempt to determineits frequency content. With AM, the signal appeared to be a sinfulness wave thats amplitude was changing with time. At the time, it was pointed out that a sine wave, by definition, has a constant bank none amplitude, and thus stopnot have a peak amplitude that varies with time. What about the sine waves frequency? It also must(prenominal) be a constant and give the bouncenot be varying with time.As was the eccentric with AM, where it turned out that our modulated wave was actually the vector sum of three sine waves, a similar situation is true for FM. An FM wave will consist of three or to a greater extent than frequency components vectorially added together to give the appearance of a sine wave thats frequency is varying with time when displayed in the time domain. A somewhat manifold mathematical analysis will yield an equation for the instantaneous potential difference of an FM wave of the form shown hereeFM(t) = EC sin(?Ct + mf sin?Mt)where EC is the rest-frequency peak amplitude, ?C and ?M represent the rest and modulating frequencies, and mf is the index of modulation. This equation represents a single low-frequency sine wave, fM, frequency modulating some other high-frequency sine wave, fC. Note that thisequation indicates that the argument of the sine wave is itself a sine wave.The Index of ModulationThe index of mod ulation, mf, is given by the following relationshipA few more than than comments about the index of modulation, mf, are appropriate. As can be seen from the equation, mf is equal to the peak deviation featured when the signal is modulated by the frequency of the modulating signal therefore, mf is a function of some(prenominal) the modulating signal amplitude and frequency. Furthermore, mf can take on any value from 0 to infinity. Its rangeis not limited as it is for AM.FM Power RelationsRecall that for an FM wave the amplitude of the signal, and hence the power, remains constant. This means that the power in the individual frequency components of the wave must add up to the transmitter output power. Furthermore, if the modulation index changes, the total power mustredistribute itself over the resulting frequency components. If there is no modulation, then mf = 0 and J0 = 1.0. Mathematically, this can be shown by the followingPrest freq = J0 power 2 PtransorPrest freq = Ptransfo r mf = 0.0.To determine the power for any individual frequency component, wecan use the following relationPn = Jn2(mf) Ptrans 4.11Furthermore, the total signal power will be given byPtotal = (J0power2 + 2J1power2 + 2J2power2 + 2J3power2 + ) Ptrans.The Effect of Noise on FMRecall AM and the opinion of noise on it. Random galvanizing variations added to the AM signal altered the original modulation of the signal. For FM, noise let off adds to the signal, but because the information resides in frequency changes instead of amplitude changes, the noise tends to have less of an effect. Expanding upon this idea a bit, one notes that the random electricalvariations encountered by the FM signal will indeed cause distortion by jittering the frequency of the FM signal. However, the change in frequency modulation caused by the jittering usually turns out to be less than the change in the amplitude modulation caused by the same relativeamplitude noise variations on an AM signal. Also unlik e AM, the effect of the frequency jittering becomes progressively worse as the modulating frequency increases. In other words, the effect of noise increases with modulation frequency. Pre-Emphasis and De-EmphasisTo compensate for this last effect, FM communication systems have incorporated a noise-combating system of pre-emphasis and de-emphasisFM times TechniquesFM signals can be generated employ either direct or verifying frequency modulation.Direct FM modulation can be achieved by directly feeding the message into the input of a VCO.For indirect FM modulation, the message signal is integrated to generate a shape modulated signal. This is used to modulate a crystal controlled oscillator, and the result is passed by a frequency multiplier to give an FM signal take aim FM GENERATIONThe simplest method for generating FM directly is to vary the frequency of an oscillator. A capacitance microphone or a varactor diode whitethorn be used as part of the oscillators frequency determin ing profit. The electrical condenser microphones capacitance varies in response to the intensity of the sound waves striking it, do the oscillators frequency vary as the amplitude of the sound varies. The varactor diodes capacitance depends on the voltage across it. Audio signals placed across the diode cause its capacitance to change, which in turn, causes the frequency of the oscillator to vary.INDIRECT FM GENERATION patch it is not doable to vary the frequency of a crystal oscillator directly, it is possible to vary its phase. The resulting PM signal can be used to hit FM. This is the basis of the Armstrong modulator.The mathematics required to analyze the Armstrong modulator completely are complex, so we will discuss only the basic circuit operation. An audio signal is passed through a preemphasis network and then an integrator, a special network whose output is the time integral of the input signal.. In this way an FM signal is generated.The Armstrong modulator cannot prod uce much deviation, so confederacy of multipliers and mixers are used to raise the carrier frequency and the deviation. The multipliers are used to multiply the carrier and the deviation. The mixers are used to decrease the carrier, while keeping the deviation constant so that additional multiplier stages can be used to fuck off more deviation.FM PerformanceFM SpectrumA spectrum represents the relative amounts of divers(prenominal) frequency components in any signal. Its like the display on the graphic-equalizer in your stereo which has leds showing the relative amounts of bass, midrange and treble. These correspond directly to increasing frequencies (treble universe the high frequency components). It is a well-k like a shot fact of mathematics, that any function (signal) can be decomposed into purely sinusoidal components (with a few pathological exceptions) . In technical terms, the sines and cosines form a complete set of functions, also know as a basis in the infinite-dimens ional vector space of real-valued functions (gag reflex). attached that any signal can be thought to be do up of sinusoidal signals, the spectrum then represents the recipe card of how to make the signal from sinusoids. Like 1 part of 50 Hz and 2 split of 200 Hz. Pure sinusoids have the simplest spectrum of all, just one componentIn this example, the carrier has 8 Hz and so the spectrum has a single component with value 1.0 at 8 Hz . The FM spectrum is considerably more complicated. The spectrum of a simple FM signal looks likeThe carrier is now 65 Hz, the modulating signal is a pure 5 Hz tone, and the modulation index is 2. What we see are multiple side-bands (spikes at other than the carrier frequency) separated by the modulating frequency, 5 Hz.There are roughly 3 side-bands on either side of the carrier. The shape of the spectrum may be explained using a simple heterodyne argument when you mix the three frequencies (fc, fm and Df) together you get the sum and difference frequ encies.The largest combination is fc + fm + Df, and the smallest is fc fm Df. Since Df = b fm, the frequency varies (b + 1) fm above and below the carrier. A more realistic example is to use an audio spectrum to provide the modulationIn this example, the information signal varies amidst 1 and 11 Hz. The carrier is at 65 Hz and the modulation index is 2. The individual side-band spikes are replaced by a more-or-less continuous spectrum. However, the extent of the side-bands is limited (approximately) to (b + 1) fm above and below. Here, that would be 33 Hz above and below, making the bandwidth about 66 Hz. We see the side-bands extend from 35 to 90 Hz, so out observed bandwidth is 65 Hz.You may have wondered why we ignored the smooth humps at the intense ends of the spectrum. The truth is that they are in fact a by-product of frequency modulation (there is no random noise in this example). However, they may be safely ignored because they are have only a consequence fraction of t he total power. In practice, the random noise would obscure them anyway.Frequency ResponseFrequency response is a specification used in amplifiers, pre-amplifiers, CD players, tape decks and other audio components to measure how uniformly it reproduces sounds from the terminal tones to the highest. An amplifier or other component should preserve the loudness relationship between various instruments and voices and should not over or under-emphasize any frequency or tone. This is known as flat frequency response.BandwidthAs we have already shown, the bandwidth of a FM signal may be predicted usingBW = 2 (b + 1 ) fmwhere b is the modulation index and fm is the maximum modulating frequency used.FM radio has a significantly larger bandwidth than AM radio, but the FM radio band is also larger. The combination keeps the number of available channels about the same.The bandwidth of an FM signal has a more complicated dependency than in the AM case (recall, the bandwidth of AM signals depen d only on the maximum modulation frequency). In FM, both the modulation index and the modulating frequency affect the bandwidth. As the information is do stronger, the bandwidth also grows.Applications of frequency modulationBroadcastingFM is commonly used at VHF radio frequencies for high-fidelity broadcasts of music and speech . approach pattern (analog) TV sound is also broadcast using FM. A intend band form is used for voice communications in moneymaking(prenominal) and amateur radio settings. The type of FM used in broadcast is generally called wide-FM, or W-FM. In two-way radio, narrowband narrow-fm (N-FM) is used to conserve bandwidth. In addition, it is used to send signals into space.SoundFM is also used at audio frequencies to synthesize sound. This technique, known as FM synthesis, was popularized by too soon digital synthesizers and became a standard feature for several generations of personal electronic computer sound cards.RadioAn example of frequency modulation. This diagram shows the modulating, or message, signal, xm(t), superimpose on the carrier wave, xc(t)The modulated signal, y(t), produced from frequency-modulating xc(t) with xm(t).A Method of Reducing Disturbances in Radio Signaling by a System of Frequency Modulation called radio FM.As , wideband FM (W-FM) requires a wider signal bandwidth than amplitude modulation by an equivalent modulating signal, but this also makes the signal more husky against noise and interference. Frequency modulation is also more robust against simple signal amplitude fading phenomena. As a result, FM was chosen as the modulation standard for high frequency, high fidelity radio transmission hence the term FM radio (although for umpteen years the BBC called it VHF radio, because commercial FM broadcasting uses a well-known(a) part of the VHF band in certain countries, expressions referencing the more beaten(prenominal) wavelength notion are still used in place of the more abstract modulation techniqu e name).A high-efficiency radio-frequency switching amplifier can be used to transmit FM signals (and other constant-amplitude signals). For a given signal specialism (measured at the receiver antenna), switching amplifiers use less battery power and typically cost less than a linear amplifier. This gives FM another advantage over other modulation schemes that require linear amplifiers, such as AM and QAM.REFRENCEShttp//en.wikipedia.org/wiki/Frequency_modulationhttp//www.tech-faq.com/frequency-modulation.shtmlhttp//www.fas.org/man/dod-101/navy/docs/es310/FM.htmhttp//www.answers.com/topic/frequency-modulation